Treatment for patients requiring orthodontic/orthopedic, orthognathic, or facial plastic surgery should include a cephalometric analysis of soft tissues. As used herein, soft tissue refers to those tissues that are less dense than bone, cartilage, and teeth, herein referred to as hard tissues. Examples of soft tissue include skin, lips, muscles and tendons.
One analysis of soft tissue cephalometric landmarks is described in Legan, et al., Soft Tissue Cephalometric Analysis for Orthognathic Surgery, J. Oral Surgery, Vol. 38, p.744–751 (October, 1980), herein incorporated by reference. Soft tissue landmarks are used to identify facial relationships, while hard tissue landmarks are used to evaluate tooth and boney relationships. Together, the soft tissue and hard tissue findings are used to establish a treatment guidance for the dentition and supporting structures to attain and maintain optimum relations in physiologic and esthetic harmony among facial and cranial structures. The soft tissue cephalometric landmarks are most important when trying to achieve desirable facial esthetics through orthodontic/orthopedic treatment, orthognathic surgery or facial plastic surgery.
FIG. 1 shows a schematic profile of a human head. Soft tissue details such as the nose, the lips, the chin, the throat and the neck as well as hard tissue structures of the chin, maxilla and mandible, occipital bone and sphenoid bone are shown. Reference numeral 100 designates a predominantly soft tissue area defined herein as the anterior facial portion. This area includes the soft tissue of the forehead, nose, lips and chin. Reference numeral 120 designates a predominantly soft tissue area defined herein as the submental-neck portion. This area includes the facial soft tissue inferior to the mandible and neck contour of a patient. Reference numeral 130 designates predominantly the soft tissue portion of the lower neck. At the intersection of submental-neck portion 120 and lower neck portion 130 is the cervical point 140. The contour of the submental-neck portion and lower neck portion is an important consideration in the esthetic look of a patient. As used herein, the contour of a patient's neck is that portion of the soft tissue extending from the chin, through the submental-neck portion 120, across cervical point 140, and extending into at least part of the lower neck portion 130 of the patient.
Numerous devices attempt to image the above-described soft tissue as well as hard tissue on the same radiograph. Referring now to FIG. 2A, a soft tissue filter screen having a straight vertical edge (i.e., an edge adapted to extend in the superior/inferior direction) has been used in connection with a cephalostat. FIG. 2A shows area 200 of a patient's head corresponding to attenuated X-rays that have passed through a prior art soft tissue filter. With this soft tissue filter screen, only the soft tissue of the anterior facial portion of a patient's head is imaged on the resulting radiograph. FIG. 2B is the radiograph of a patient's head taken with a cephalostat using the soft tissue filter screen reflected in FIG. 2A. This screen having a vertical edge across the entire height of the imaged area fails to attenuate X-rays passing through the submental-neck portion and lower neck portion of the patient's head. The resulting radiograph shows a darkened overexposed area where the patient's neck line would be.
One attempted solution to view the anterior facial portion and the submental-neck portion of a patient's head on the same radiograph would be to widen the soft tissue filter screen. FIG. 3A shows a reflection of a wide soft tissue filter screen with reference numeral 300 designating the area of the patient's head corresponding to attenuated X-rays from the soft tissue filter screen. A problem with widening the soft tissue filter screen is that the filter then blurs hard tissue landmarks. FIG. 3B is a radiograph of a patient's head taken with a cephalostat using a wide soft tissue screen. Line 310 marks the posterior edge of the soft tissue filter. As can been seen, only a part of the submental-neck portion has been imaged, the hard tissue landmarks around the teeth have been blurred and still, the cervical point and all of the neck contour is not visible.
A different approach to solving the problem of visualization of the soft tissue of the anterior facial and submental-neck portion (and possibly the lower neck portion) congruently with hard tissue structures on the same radiograph is through the use of a face shield. Shown in FIG. 4A is a hand-held face shield 400 contoured to a patient's face. One disadvantage of this type of face shield is that each patient's face is uniquely shaped and many different sized face shields would be needed. Secondly, the face shield must be held in place by the patient. The clarity of the radiograph depends upon how steady a patient can hold the face shield against his face. In this regard, the face shield is impractical for use with young children. Yet a further drawback to the face shield shown in FIG. 4A is that it imparts a drastic line of demarcation on the radiograph from the leading edge 410 of face shield 400. FIG. 4B shows a radiograph of a patient's head using the face shield 400. Demarcation line 420 is clearly visible, and hard tissue blurring of the front teeth and anterior boney landmarks still occurs.
What is needed therefore is an adaptable system for attenuating X-ray energy over soft tissue cephalometric landmarks of the anterior facial portion and submental-neck portion of a patient's head while maintaining the X-ray energy over hard tissue landmarks permitting imaging of both soft and hard tissue landmarks on the same radiograph.